W3C home > Mailing lists > Public > public-xmlhypermedia@w3.org > July 2012

RE: Hypermedia - Why

From: Rushforth, Peter <Peter.Rushforth@NRCan-RNCan.gc.ca>
Date: Fri, 27 Jul 2012 12:39:54 +0000
To: David Carlisle <davidc@nag.co.uk>
CC: "public-xmlhypermedia@w3.org" <public-xmlhypermedia@w3.org>
Message-ID: <1CD55F04538DEA4F85F3ADF7745464AF1AE2BD5B@S-BSC-MBX4.nrn.nrcan.gc.ca>

Not sure we're making progress in this thread anymore.  

I meant to put up the wiki page with the "why" bit, so I'll do that next.

I'll also  try to put some of these ideas in the wiki to capture them for further discussion under issues, or design considerations.

See in line.



From: David Carlisle [davidc@nag.co.uk]
Sent: July 27, 2012 7:00 AM
To: Rushforth, Peter
Cc: public-xmlhypermedia@w3.org
Subject: Re: Hypermedia - Why

>It's fine for Atom (or HTML) to do this, they are languages/vocabularies
defined using XML syntax. That doesn't mean that it is OK for XML to do it.

XML would not be doing it, it would be giving those vocab designers the tools
to do it with.

>Whatever words you prefer, XML is at a different level than atom or html.

>XML should as far as possible not pollute the vocabularies defined using
that syntax by forcing element and attribute names.

I agree with the "as far as possible" idea.  Namespaces already allows this, 
and I don't think another spec is required to allow devs to create their own names etc.

>> Atom, for instance, does not use a schema, per se, just a public
>> specification with required / permitted content layout. I would say
>> it is a best practice for hypermedia design.

>Same is true of HTML in the latest versions.
That is the avenue of development we should target.  MicroXML can fight its own
battles, though, which will be bigger than the xml: namespace, I think.

> As long as it is not the _only_ position, we can still talk.

yes cuts both ways though, you should also be prepared to contemplate a
mechanism that lets you declare that attributes have hypermedia
properties that does not use the blunt instrument of predefining certain
attribute names.

Do you have a mechanism in mind?  I thought Liam's no namespace prefix namespaces idea might work.  


As I mentioned to him, the mechanism would not require a specific change to the xml: namespace, but could be accomplished with the application of the hypermedia vowels in the xml: namespace.  Everybody wins!

>> We should ask the hypermedia community what *they* think. Not the
>> XML community, strictly, although there is obviously an
>> intersection.

>I am not sure who you see as being the "hypermedia community"  but HTML
would be nice to have some of the html community talking here, perhaps you know some
of them, and could invite them to discuss? 

But, the hypermedia part of the name of this community group has attracted a number of people who I know are experts in hypermedia too, so we are in good company anyway.

>the fact that you could not model
<img src="foo" longdesc="bar"/>
>in xlink because it requires two URI on the same element was a _major_
>reason for blocking the adoption of xlink in (X)HTML at the time.

I can see the need/desire to minimize markup, but longdesc does not seem to have won out in the end:

I would think 
<img src="foo"><link href="bar" rel="describedby"/></img>

might work too.  Not sure what the best practice is now, probably something driven by accessibility needs, I would think.

>> If you want to say attribute foo="example.com" is a link of a
>> certain type, you should define a schema type representing that and
>> then apply that schema to the instance. (Or if not XSD specify a
>> different annotation mechanism). What you should not do is say "if
>> you want to make a link the attribute has to have fixed name
>> xxxxx".
> I personally have nothing against XSD, nor schemas of any kind in
> general. In fact, the bugzilla bug I wrote included a schema to
> describe these vowels. I'm a pointy bracket guy! But I think schemas
> and namespaces are what we want to avoid in this case. If you want to
> do that with your vocabulary, so as to have control over the names of
> attributes, elements, what have you, go ahead, the facilities are
> there already in XML. What we want here are some hypermedia
> affordance vowels which reflect the architectural style of the web,
> as we know it today, and that we can refer to in our vocabularies,
> _by specification_, not schema.

>It doesn't have to be a schema: just some declarative method that lets
>you say which attributes have which properties.
>The HTML group at the time proposed an extended css declaration syntax
as I recall as a counter-proposal to xlink.

>ah found it: "clink" eg this discussion


>Or the original opera proposal from 2000 that states right up front:

> There are three key differences between Clink and Xlink. First,
> Clink is a much simpler language not capable of describing the more
> advanced features of Xlink. Second, Clink does not require markup
> languages to change their syntax in order to describe linking
> behavior. Third, Xlink has some functionality which goes beyond
> Xlink, namely HTML's longdesc attribute and base element.


>You see, nothing I have said in this thread has not been said dozens of
times before by different people in different decades.

Thanks for the links, they are very valuable, as is your knowledge of the domain.  

I believe they found the Golden Giant Mine (Hemlo) essentially beside  the TransCanada Highway where people had been 
driving for generations, so it may be worthwhile reviewing some of the ground 
that has been covered.

I personally like Liam's unobtrusive namespaces idea, and I think it could work.  All it needs
is a set of general hypermedia linking vowels to point to the namespace file in a RESTful manner:

<mydocument xml:href="ns.x" xml:type="application/ns+xml" xml:rel="namespaces" />.  If the rel and type values became
well enough known, I bet it would not even require a resource to be located at @xml:href.


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Received on Friday, 27 July 2012 12:40:23 UTC

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